The present invention relates to atomic absorption spectrophotometers, and more particularly to an atomic absorption spectrophotometer suitable for quantitatively determining a very small amount of metallic element dissolved in an aqueous solution.
In an atomic absorption spectrophotometer, as described in U.S. Pat. No. 4,377,342, a desired element contained in a liquid sample is converted by an atomizer such as a graphite tube into atomic vapor, and the atomic vapor is irradiated with light from a light source, to quantitatively determine the desired element on the basis of the degree of absorption of light by the atomic vapor. In such a case, the density of atomic vapor within the graphite tube increases as the concentration of the desired element in the sample is larger, but the absorption of light by the atomic vapor saturates at an absorbance of about 2.0, though this value varies slightly, depending upon the kind of the desired element. Thus, it is impossible to quantitatively determine the desired element which is contained in the sample at concentrations greater than a value.
In order to make it possible to quantitatively determine a desired element which is contained in a liquid sample at high concentrations and causes the above saturation phenomenon, an analytical method is proposed in the above-referred U.S. Pat. No. 4,377,342. In this method, attention is paid to the absorbance vs. time curve (that is, absorption profile) of the desired element, and the element is quantitatively determined on the basis of the time width of the absorption profile at a predetermined absorbance. That is, the analytical method using a time width of absorption profile is based upon a fact that the time width of absorption profile at the predetermined absorbance increases with increasing concentration of the desired element. In this method, however, the gradient of tangent to a working curve decreases greatly with increasing concentration of the desired element, as shown in FIGS. 6 and 7 of the above-referred U.S. Patent, and hence it is not always possible to determine the desired element accurately.